Teste si le login existe dans l'annuaire LDAP !

src/UnicaenOauth/OAuth2/Adapter/StorageAdapter.php

@@ -40,11 +40,13 @@ class StorageAdapter extends PdoAdapter
             return parent::checkPassword($user, $password);
         }
 
-        $user = $this->getUser($username);
-
+        if ($user = $this->getUser($username)) {
             return $this->checkPassword($user, $password);
         }
 
+        return false;
+    }
+
     /**
      * Redéfinition.
      *